1. Field of the Invention
This invention relates to an air mix controller appropriate for an automobile air conditioner using a plurality of actuators of the same kind.
2. Description of the Related Art
A control system wherein door driving actuators are unified all to PBR actuators containing ICs for comprehensively controlling the actuators by an auto amplifier using serial communication over one communication line, which will be hereinafter referred to as "air conditioning LAN system, for decreasing the number of harnesses and reducing system costs is developed at present as an actuator control system used for an automobile air conditioner.
By the way, a method as shown in a flowchart in FIG. 3 is available as a conventional air mix control method in general automobile air conditioners other than the air conditioning LAN system. Here, only a brief description is given because a detailed description will be given later. Generally, the main body of an automobile air conditioner is made up of an intake unit for selectively introducing inside or outside air of an automobile, a cooling unit containing an evaporator forming a cooler cycle, and a heater unit containing a heater core circulating engine cooling water for controlling the heat air amount with an air mix door so as to adjust a temperature.
To control an actuator for driving the air mix door (air mix door actuator), an auto amplifier first inputs various data values, such as setup temperature, cabin temperature, outside air temperature, solar radiation amount, and suction temperature (air temperature at the cooling unit exit, namely, temperature of air sucked into the heater unit making a temperature adjustment) at step S21 and calculates a target temperature in the cabin (target room temperature) according to a predetermined calculation expression at step S22, then inputs the door opening value detected by PBR (PBR value) at step S23 and calculates the current opening of the air mix door, X, using a predetermined calculation expression according to the PBR characteristic considering a link, etc., at step S24. Then, at step S25, the auto amplifier calculates deviation S value according to a predetermined calculation expression from the target room temperature found at step S22 and the door opening X found at step S24.
When the S value is found, the auto amplifier compares the S value with .+-.2.degree. C. at step S26. As the result of the comparison, if the S value is less than -2.degree. C., the auto amplifier drives the actuator to the cool side at step S27; if the S value lies in the range of -2.degree. C. to +2.degree. C., the auto amplifier holds the actuator at step S28; if the S value is greater than +2.degree. C., the auto amplifier drives the actuator to the hot side at step S29. At the termination of steps S26 to S29, the auto amplifier returns to step S21 and repeats execution of step S21 and the following steps in a predetermined short control cycle.
However, such an air mix control method cannot be applied to the air conditioning LAN system. The reason why the method cannot be applied to the system is as follows: In the air conditioning LAN system, the auto amplifier simply transmits control data (target position) to actuators and the actuators perform specific positioning of doors on their own while monitoring the current positions according to the target position data, thus the detected PBR value is processed in the air mix door actuator and is not fed back into the auto amplifier.
Therefore, to construct the air conditioning LAN system, a new air mix control method (control program) for the system needs to be designed. At this time, if the minimum change is only required based on the conventional control program described above (see FIG. 3), it is extremely desirable because the conventional technique (control system) is followed, whereby the number of development steps is decreased and the control program reliability is also maintained.